1. Sexual Reproduction and Genetics
Chapter 10
Sexual Reproduction and Genetics

2. Meiosis Chromosomes and Chromosome Number
Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes
Homologous chromosomes—one of two paired chromosomes, one from each parent

3. Meiosis Chromosomes and Chromosome Number Same length
Same centromere position
Carry genes that control the same inherited traits

4. Meiosis Haploid and Diploid Cells
An organism produces gametes to maintain the same number of chromosomes from generation to generation.
Human gametes contain 23 chromosomes.
A cell with n chromosomes is called a haploid cell.
A cell that contains 2n chromosomes is called a diploid cell.

5. Meiosis Meiosis I The sexual life cycle in animals involves meiosis.
Meiosis produces gametes.
When gametes combine in fertilization, the number of chromosomes is restored

7. Meiosis Stages of Meiosis I
Reduces the chromosome number by half through the separation of homologous chromosomes
Involves two consecutive cell divisions called meiosis I and meiosis II

8. Meiosis Meiosis I Interphase Chromosomes replicate.
Chromatin condenses.

9. Meiosis Meiosis I Prophase I Pairing of homologous chromosomes occurs.
Each chromosome consists of two chromatids.
The nuclear envelope breaks down.
Spindles form.

10. Meiosis Meiosis I Prophase I
Crossing over produces exchange of genetic information.
Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

11. Meiosis Meiosis I Metaphase I
Chromosome centromeres attach to spindle fibers.
Homologous chromosomes line up at the equator.

12. Meiosis Meiosis I Anaphase I
Homologous chromosomes separate and move to opposite poles of the cell.

13. Meiosis Meiosis I Telophase I The spindles break down.
Chromosomes uncoil and form two nuclei.
The cell divides.

14. Meiosis Meiosis II Prophase II
A second set of phases begins as the spindle apparatus forms and the chromosomes condense.

15. MEiosis Meiosis II Metaphase II
A haploid number of chromosomes line up at the equator.

16. Meiosis Meiosis II Anaphase II
The sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell.

17. Meiosis Meiosis II Telophase II
The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

18. Meiosis
Meiosis II
Cytokinesis results in four haploid cells, each with n number of chromosomes.

19. Meiosis The Importance of Meiosis
Meiosis consists of two sets of divisions
Produces four haploid daughter cells that are not identical
Results in genetic variation

20. Meiosis Meiosis Provides Variation
Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.
Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

21. Meiosis Sexual Reproduction v. Asexual Reproduction
The organism inherits all of its chromosomes from a single parent.
The new individual is genetically identical to its parent.
Sexual reproduction
Beneficial genes multiply faster over time.

22. Meiosis How Genetics Began
The passing of traits to the next generation is called inheritance, or heredity.
Mendel performed cross-pollination in pea plants.
Mendel followed various traits in the pea plants he bred.

23. Meiosis
The parent generation is also known as the P generation.

24. Meiosis
The offspring of this P cross are called the first filial (F1) generation.
The second filial (F2) generation is the offspring from the F1 cross.

25. Meiosis Mendel studied seven different traits. Seed or pea color
Flower color
Seed pod color
Seed shape or texture
Seed pod shape
Stem length
Flower position

26. Meiosis Genes in Pairs Allele Dominant Recessive
An alternative form of a single gene passed from generation to generation
Dominant
Recessive

27. Meiosis
Dominance
An organism with two of the same alleles for a particular trait is homozygous.
An organism with two different alleles for a particular trait is heterozygous.

28. Meiosis Genotype and Phenotype
An organism’s allele pairs are called its genotype.
The observable characteristic or outward expression of an allele pair is called the phenotype.

29. Meiosis Mendel’s Law of Segregation
Two alleles for each trait separate during meiosis.
During fertilization, two alleles for that trait unite.
Heterozygous organisms are called hybrids.

30. Meiosis Monohybrid Cross
A cross that involves hybrids for a single trait is called a monohybrid cross.

31. Meiosis Dihybrid Cross
The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.
Dihybrids are heterozygous for both traits.

32. Meiosis Law of Independent Assortment
Random distribution of alleles occurs during gamete formation
Genes on separate chromosomes sort independently during meiosis.
Each allele combination is equally likely to occur.

33. Meiosis Punnett Squares
Predict the possible offspring of a cross between two known genotypes

34. Meiosis Punnett Square—Dihybrid Cross
Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.
The resulting phenotypic ratio is 9:3:3:1.

35. Meiosis Genetic Recombination
The new combination of genes produced by crossing over and independent assortment
Combinations of genes due to independent assortment can be calculated using the formula 2n, where n is the number of chromosome pairs.

36. Meiosis
Gene Linkage
The linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently.

37. Meiosis
Polyploidy
Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.
A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes.